Subjects unable to support their own weight due to a lower extremity impairment may resort to crutches or wheel chairs to move about. However, crutches and wheel chairs may be undesirable because of the limitations they impose on a subject's ability to use their hands. In addition, crutches and/or wheel chairs may incompletely restore mobility, and/or may be untenable in an older person due to decreased upper body strength and/or poor balance in the case of crutches.